1. Field of the Invention
The present invention relates to a liquid-crystal display, or more particularly, to a liquid-crystal display capable of not giving a sense of incompatibility to viewers at the time of displaying a video signal indicating an aspect ratio different from the size of a screen of a liquid-crystal panel.
2. Description of the Related Art
In recent years, a television set using an image receiving tube has been used as an information transmission means in the advanced information age. A liquid-crystal television set using a liquid-crystal module is attracting attention in past years. In particular, a liquid-crystal projector using a liquid crystal is under earnest research and development. In the field of broadcast systems, the research and development of a Hi-Vision system or EDTV-2 system (aspect ratio of 16:9) is under way in parallel with that of a conventional NTSC system (aspect ratio of 4:3). Experimental broadcasting based on the Hi-Vision system has been started. Accordingly, a device having an aspect ratio of 16:9 has been developed as a liquid-crystal module. Besides, products offering the aspect ratio of 16:9 have made their debuts.
FIG. 5 is a block diagram showing a related art of such a liquid-crystal display.
In FIG. 5, a video signal a5, horizontal synchronizing (hereinafter sync) signal b5, and vertical sync signal c5 sent from a video signal processing circuit that is not shown are introduced into input terminals 81, 82, and 83.
The video signal a5 introduced into the input terminal 81 is supplied to a sample and hold circuit 92. The horizontal sync signal b5 introduced into the input terminal 82 is supplied to a clock generator 86 of a clock oscillator circuit 85. The vertical sync signal c5 introduced into the input terminal 83 is supplied to a clock circuit 87 for a vertical-direction shift register (hereinafter referred to as a V clock circuit 87) of the clock oscillator circuit 85.
The clock oscillator circuit 85 comprises the clock generator 86, V clock circuit 87, a voltage-controlled oscillator (VCO) 88, and a clock circuit 89 for a horizontal-direction shift register (hereinafter referred to as an H clock circuit 89).
The VCO 88 has an oscillatory frequency thereof set to a frequency dependent on the number of pixels in a liquid-crystal panel 95, and supplies an oscillatory signal thereof to the clock generator 86. The clock generator 86 outputs the oscillatory signal sent from the VCO 88 synchronously with the horizontal sync signal b5 supplied through the input terminal 82, and supplies a clock d5 to the H clock circuit 89.
The H clock circuit 89 obtains a fraction of 1/n (n denotes a natural number) of the frequency of the clock d5, produces a clock e5, and supplies the clock e5 to a clock terminal of a horizontal-direction shift register (hereinafter referred to as an H shift register) 84 and to the V clock circuit 87. The V clock circuit 87 obtains a fraction of 1/m (m denotes a natural number) of the frequency of the clock e5, outputs an output resulting from frequency division synchronously with the vertical sync signal c5 supplied through the input terminal 83, and thus supplies a clock f5 to the clock terminal of the V shift register 91.
The H shift register 84, sample and hold circuit 92, and an X driver 93 are designed to have the number of bits agreeing with the number of pixels in the horizontal direction of the liquid-crystal panel 95. The H shift register 84 shifts the clock e5 continuously, and outputs a resultant pulse as a sample pulse successively through the bits associated with the pixels in the horizontal direction. The video signal a5 is supplied to the sample and hold circuit 92 through the terminal 81. According to the timing of the sample pulse to be input in relation to each pixel, pulses of a video signal associated with the pixels in the horizontal direction are sampled and held. When the video signals representing one line have been held in the sample and hold circuit 92, the X driver 93 applies the held video signals representing one line to data lines (not shown) in the liquid-crystal panel 95.
The V shift register 91 and a Y driver 94 have the number of bits agreeing with the number of pixels in the vertical direction of the liquid-crystal panel 95. The V shift register 91 shifts the input clock f5 continuously, and outputs a resultant pulse to the Y driver 94 successively through the bits associated with the pixels in the vertical direction. The Y driver 94 applies the output of the V shift register 91 as a scan signal to scan lines in the liquid-crystal panel 95.
In the liquid-crystal panel 95, a liquid-crystal pixel is formed between each pair of data lines and scan lines which are arranged in the form of a matrix. Video signal data is written in liquid-crystal pixels selected by the X driver 93 and Y driver 94, whereby the transmittance of the liquid crystal is controlled. Located on the back side of the liquid-crystal panel 95 is a light source (not shown). Light emanating from the light source is transmitted by the liquid-crystal panel 95 and thus converted into picture light. In the case of this kind of projection type liquid-crystal display, light transmitted by a liquid-crystal panel is enlarged and projected on a screen by a projection lens.
By the way, when the aspect ratio of the liquid-crystal panel 95 is the same as the one indicated by a video signal to be displayed on the panel, a display picture appears properly. However, if the aspect ratio of the liquid-crystal panel 95 is different from the one indicated by a video signal, a problem occurs. This will be described in conjunction with FIG. 6.
In FIG. 6, reference numeral 101 denotes a video signal indicating an aspect ratio of 4:3. When this kind of video signal is displayed on the liquid-crystal panel 95 having an aspect ratio of 16:9 as it is, the video signal appears as a picture 102 stretching sideways and gives a sense of incompatibility to viewers.
For resolving this kind of sideways stretch phenomenon, for example, as shown in FIG. 7, a video signal indicating the aspect ratio of 4:3 is stretched uniformly in the vertical and lateral directions, and then displayed in the liquid-crystal panel 95 having the aspect ratio of 16:9. Consequently, the video signal is displayed as a picture 103 with a correct roundness. However, in this case, there is a drawback that video information coincident with the top and bottom of a screen is lost.
As shown in FIG. 8, it is also conceivable that completely different pictures (for example, black pictures 105 and 106) are appended to the right-hand and left-hand sides of a picture represented by a video signal indicating the aspect ratio of 4:3 so that a picture 104 having a correct roundness can be displayed. In this case, however, pictures unrelated to an original picture are displayed to give a sense of incompatibility to viewers. Besides, a wide liquid-crystal panel cannot be utilized effectively.
In other words, when the aspect ratio of a liquid-crystal panel is different from the one indicated by a video signal to be displayed on the panel, a picture may be distorted, information coincident with upper and lower parts of a screen may be lost, or measures must be taken by displaying unrelated pictures. Consequently, a sense of incompatibility is given to viewers.